A comparable cutting tool is disclosed in EP-B-0 385 280. The cutting edge of the tool moves in a radial direction of advance during parting in machining the interior wall of a drill hole. In the process, the cutting edge must be positioned with the greatest accuracy possible in a diametral advance plane extending parallel to this radial direction of advance. Only with the cutting edge in this position is an optimal clearance angle obtained. Spacing the cutting edge away from the diametral advance plane results in clearance angles which may lead to unfavorable results in metal removal, such as vibration of the tool. For this reason, very precise rotary positioning of the tool in the tool holder must be achieved. The position of the tool must not vary appreciably when a load is applied to the tool. Distances between the cutting edge and this diametral plane are especially critical in the case of drill holes of small diameter which are to be machined, since, in this situation, even a slight variation of such spacing from zero results in major change in the clearance angle. To prevent such occurrence, the cutting tool disclosed in the European prior publication has on its clamp component clamping surfaces which at least to some extent converge toward each other. By these surfaces, the cutting tool may be secured on a processing machine, such as one in the form of a lathe. It is being possible to bring such converging surfaces in contact with correspondingly converging contact surfaces of the tool holder. By the mould closure referred to, a precisely defined rotary position of the disclosed clasp tool may be achieved in that radial enlargement in the seating recess in the tool holder. The radial projection on the shaft component of the clasp tool results through the action of the clamping means in rigorously defined application of the clamping surfaces of the radial projection to the contact surfaces of the enlargement. Change in the cutting position perpendicular to the diametral advance plane, when load is applied to the tool, is prevented, since the rotary position of the cutting tool relative to the tool holder is ensured in that application of the clamping surfaces to the application surface acts on a radius enlarged in relation to the radius of the receptacle bore.
To permit machining of drill holes of extremely small diameter, it has been recognized in the disclosed solution as advantageous to configure the clasping tool as one piece. Other advantages to this end are achieved if the clasping tool is formed of a cutting alloy, since, because of the large elasticity modulus of cutting alloy tools, the cutting edge remains precisely in the position originally set even under relatively high loads, so that change in the cutting position relative to the diametral advance plane when a load is applied is virtually eliminated.
It has been found, however, that, despite the measures described, the disclosed cutting tool approaches its limits when drill holes of extremely small diameter, less than one millimeter, such as 0.7 mm, are to be machined. Despite the advantageous tool holding, the integrated configuration of the tool, and its construction by use of cutting alloy materials, these disclosed measures do not make it possible to advance in this range of operation with boring diameters smaller than 1 mm to achieve the machining qualities desired.
EP-A-0 947 267 discloses a generic tool having a holder in which a plate with three cutting edges may be secured by means of a threaded connection. The free end of the holder on which the cutting tool may be seated has recesses by means of which reinforcing ribs are produced. Despite the holder components reduced by the cut-out recesses, such good reinforcement is obtained thereby for the cutting plate that vibrations impairing the machining quality during machining are absorbed and the holder is reinforced. Because of the flat application of the plate with three cutting edges on the end of the holder and the disclosed possibility of fastening by means of a screw connection, misadjustment of the machining edge may occur, and the configuration of the disclosed solution is so large that application of this for drill holes of extremely small diameter is not possible.